1. Field of the Invention
This invention relates to electrical power production and conversion in general, and in particular, to a power supply useful for powering an ion thruster engine.
2. Related Art
Electrostatic ion thruster engines for spacecraft require a source of high voltage DC power to provide an accelerating voltage for the propellant ions created within the engine. These ions are accelerated to a high velocity by the high voltage and then expelled from the engine, thereby providing a reactive thrust to the vehicle to which the engine is mounted. For some space vehicles incorporating ion thruster engines, it is therefore typically necessary to provide a power converter for converting power from a relatively low voltage, multiphase AC source, such as a multiphase alternator, to a relatively high voltage DC output to the engine in an efficient, reliable way. Additionally, it is desirable for the electronic components of the converter to be capable of operating reliably in the high radiation environment of space.
An AC-to-DC converter is typically employed as a so-called “front-end” power supply in many electronic power systems. Various topologies are known for converting the AC power output of a generator or an alternator, to DC power, and these typically involve one or more stages of rectification, and, where the final DC voltage required is greater than the peak voltage supplied by the AC source, one or more stages of transformation, typically effected with either transformers and/or DC-to-DC converters.
In the case of spacecraft equipped with ion thruster engines, the AC source can be a multiphase alternator driven by a nuclear-reactor-powered turbine, and is typically located remotely from the ion engine itself. This requires conveying the alternator power to the engine over relatively long distances, e.g., 30-50 ft. Thus, while it is theoretically possible to provide an alternator having an output voltage that is the same or greater than the high voltage required by the engine, e.g., 4000-5000 VDC, this is impracticable because of the shielding problems encountered, such as arcing and insulator degradation, in conveying such high voltages over such relatively long distances. Therefore, as a practical upper limit, the maximum voltage that can be reliably conveyed over such distances without encountering shielding problems is about 400-500 V RMS. It is therefore preferable to confine the high voltage portions of the power converter, including the voltage transformation portions, to locations that are relatively close to the engine and thereby minimize high voltage shielding problems.
In addition to the foregoing considerations, it will be understood that even low current versions of transformers capable of producing high voltages must be large and heavy, especially if used in the hard vacuum of space, because of the power handling and maximum flux capability required of these transformers. On the other hand, DC-to-DC converters that rely on “choppers,” i.e., active devices, such as transistors, can be complex, and are particularly susceptible to radiation damage in the space environment.
Accordingly, a long felt but as yet unsatisfied need exists for a simple, efficient, reliable, and light weight power converter that is capable of coupling the power from the output of a lower voltage multiphase AC alternator to a source of higher voltage DC power in a form suitable for powering an electrostatic ion thruster engine. Additionally, the desired converter should have a high power factor in the transmission of power to the engine, utilize only components having a high tolerance to space radiation environments, and have a power and output voltage that can be easily and precisely controlled.